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Noise Exposure Math for Factory Floors: A Small Python Helper

#python #tutorial #engineering #safety

Compressors, presses, looms and DG sets can push a shop floor well past safe noise levels. Here is a small Python helper to estimate how long people can stay in an area and how much hearing protection helps.

Allowed time at a given level

The NIOSH recommended limit is 85 dBA for 8 hours, with a 3 dB exchange rate: every 3 dB more halves the allowed time.

def allowed_hours(dba, limit=85, exchange=3):
    return 8 / 2 ** ((dba - limit) / exchange)

for level in (85, 88, 91, 94, 100):
    print(level, "dBA ->", round(allowed_hours(level), 2), "h")
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85 dBA -> 8.0 h
88 dBA -> 4.0 h
91 dBA -> 2.0 h
94 dBA -> 1.0 h
100 dBA -> 0.25 h
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Daily noise dose

Most people move between areas during a shift. The dose adds up each part: hours spent divided by hours allowed at that level. Over 100% means too much.

def daily_dose(exposures):  # list of (dBA, hours)
    return 100 * sum(h / allowed_hours(l) for l, h in exposures)

shift = [(92, 2), (86, 4), (80, 2)]
print(round(daily_dose(shift)), "%")  # 197 %
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Estimating protection

The NRR on a label is measured in a lab, so NIOSH suggests derating it: 25% off for earmuffs, 50% for foam plugs and 70% for other plugs, then subtracting 7 dB when you work in dBA.

DERATE = {"earmuff": 0.25, "foam_plug": 0.50, "other_plug": 0.70}

def protected_level(dba, nrr, kind):
    effective = nrr * (1 - DERATE[kind]) - 7
    return dba - max(effective, 0)

print(protected_level(95, 27, "earmuff"))  # 81.75
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Caveats

Rules differ by country (OSHA, for example, uses 90 dBA with a 5 dB exchange rate), so use your local limits. Measure real levels with a sound level meter, and use the rating printed on the protector you actually buy. This is a planning tool, not a substitute for a proper noise survey.

PackForge supplies disposable plugs, corded plugs and over-ear muffs for high-noise areas such as compressor rooms, presses and DG sets: Ear muffs and ear plugs.

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